1. Technical Field
One or more embodiments of the invention generally relate to systems and processes for recovering natural gas liquids (NGL) from a gas stream using a closed-loop mixed refrigerant cycle.
2. Description of Related Art
In recent years, higher energy prices have prompted oil and gas producers to utilize heavier hydrocarbon materials as feedstocks to produce fuels and other end products. In doing so, general reliance on “cracking” processes that break long-chain, high carbon number molecules to smaller, more utilizable hydrocarbons, has increased. As a result, more off-gas streams from these cracking processes are produced that comprise higher concentrations of hydrogen and olefins, which may be desirable to recover for subsequent use. In particular, the recovery of C2 through C6 olefins is increasingly desirable in order to provide valuable feedstocks for the petrochemical industry.
Conventional processes for separating ethylene and heavier components (e.g., C2+ components) from a gas stream currently are plagued by a variety of drawbacks. For example, many C2+ recovery processes must be carried out at very low temperatures (e.g., less than −180° F.) and/or high pressures (e.g., above 600 psig). As a result, these processes are capital intensive and expensive to operate and maintain. In addition, the severe operating conditions required by conventionally-designed systems can result in formation and accumulation of unique byproducts, such as “blue oil,” that are both highly undesirable and potentially hazardous.
Thus, a need exists for a process and systems for recovering natural gas liquids (NGL) from a feed gas stream that minimize compression requirements and byproduct formation, while maximizing recovery of valuable products. The system should be both robust and operationally flexible to handle variations in both feed gas composition and flow rate, and should be simple and cost-efficient to operate and maintain.